1. Field of the Invention
The present invention relates generally to a Digital Pre-Distortion (DPD) power amplifier in a multiple antenna wireless communication system. More particularly, the present invention relates to a DPD power amplifier sharing a DPD feedback path in a multiple antenna wireless communication system.
2. Description of the Related Art
A DPD power amplifier has been designed for improving a non-linear characteristic of a power amplifier. The DPD power amplifier has also been designed to provide a linear relationship between an input and an output signal of the DPD power amplifier by distorting a digital signal before amplifying the digital signal. The structure of the DPD power amplifier for a single transmission path is illustrated in FIG. 1.
As illustrated in FIG. 1, the DPD power amplifier includes a digital up-converter 102, a Peak to Average Power Ratio (PAPR) controller 104, a DPD processor 106, a Digital to Analog Converter (DAC) 108, a high power amplifier 110, a coupler 112, a Band Pass Filter (BPF) 114 and a DPD feedback path 116.
An input baseband digital signal is up-converted into a digital signal in a Radio Frequency (RF) band by the digital up-converter 102. The digital signal in the RF band has a low PAPR by the PAPR controller 104. Also, the digital signal is pre-distorted by the DPD processor 106 and converted into an analog signal by the DAC 108 and amplified by the high power amplifier 110. The signal amplified by the high power amplifier 110 is filtered by the BPF 114 and transmitted via an antenna. Also, a portion of the signal amplified by the high power amplifier 110 is extracted by the coupler 112 and provided to the DPD processor 106 via the DPD feedback path 116. The DPD processor 106 also performs pre-distortion according to the output of the high power amplifier 110 provided via the DPD feedback path 116.
When a transmission end has a plurality of transmission paths, that is, in the case where a multiple antenna technique is applied, a construction for independent DPD for each transmission path is included. In other words, the number of DPD processors 106 and DPD feedback paths 116 are equivalent to the number of transmission paths. Here, the DPD feedback path 116 includes many elements, such as an RF amplifier, an Intermediate Frequency (IF) amplifier, a mixer, an Analog to Digital Converter (ADC), a filter, etc. Since the construction for DPD, for example, the DPD feedback path 116 independently exists on each of the transmission paths, the size and costs of the transmission end increases.
Therefore, a need exists for an apparatus and method for decreasing a size and costs of a plurality of transmission paths of a DPD power amplifier in a multiple antenna wireless communication system.